How to map

If you know whether or not the hospital in question is equipped to deal with emergencies - this is called A&E (accidents and emergencies) in the UK and ER (emergency room) in the US - then you can add emergency=* with a value of "yes" or "no".

You may see the amenity=hospital tag on an area alongside a building=yes (or building=hospital tag), where there is a single building outline for the hospital, however the normal approach is draw an area enveloping the hospital grounds and one or more areas with building tags inside this area. It's quite common to have a large hospital campus with multiple buildings. Note that the buildings should not carry the amenity=hospital tag. One feature, one OSM element. One hospital, one area tagged amenity=hospital. This is in line with recommendations for other types of institution such as schools and universities.

Building entrances can be mapped with a node on the building outline, with the tag entrance=yes. Likewise an entrance to the grounds of the hospital might be mapped as a node with barrier=*. This node would also be part of a footway or service road from the main road network so that it is possible to route to the entrance of the hospital.